1. Field of the Invention
The present invention relates to a pinch roller apparatus used for a tape recorder, a VTR or the like.
2. Description of the Background Art
A pinch roller apparatus includes a rotationally driven capstan, and a pinch roller including a roller body which is pressed against the capstan. A tape is pinched between the capstan and the roller body which are in pressure contact with each other and moved in a prescribed direction.
General requirements for the pinch roller include tape running stability and durability of the pinch roller itself. One factor for determining the tape running stability is the self-alignment function of the pinch roller. By the self-alignment function, any error in parallelism between the axis of the capstan and the pinch roller, which is inevitable in design and manufacturing, is absorbed by the play in the direction of inclination of the roller body of the pinch roller with respect to the roller shaft, whereby the axis of rotation of the roller body is made parallel to the axis of rotation of the capstan. When the pinch roller does not have such a self-alignment function or the pinch roller has a poor self-alignment function, degrading of the running stability of the tape occurs. For example, the tape pinching pressure may be biased, resulting in an irregular stretching of the tape. The tape may possibly come off of the pinch roller or the tape may deviate in the upward or downward direction, or the running speed of the tape may fluctuate, resulting in an increase in the wow and flutter.
In a typical structure of a conventional pinch roller, a roller body having an elastic body such as rubber fixed to the outer peripheral surface of a cylindrical sleeve is rotatably attached to a roller shaft by means of a ball bearing. In such a structure, very precise and small ball bearings are necessary, and hence the manufacturing costs of the pinch roller are high.
In view of the foregoing, the application of a plain bearing formed of a resin or a sintered metal which has a simple structure and is inexpensive as a pinch roller instead of the use of ball bearings has been proposed. FIG. 3 is an illustration showing a self-alignment function of the pinch roller employing a plain bearing. When roller shaft 1 is inclined with respect to a capstan C, roller body 3 is inclined with respect to roller shaft 1 because of a clearance provided between bearing 2 and roller shaft 1, so that the axis of rotation of the roller body becomes parallel to the axis of the capstan. In the figure, "T" represents a tape, 31 represents a metal sleeve and 34 represents a cylindrical elastic body.
However, when a large clearance is provided between bearing 2 and roller shaft 1, only the upper or lower end of the bearing will be brought into contact with the roller shaft, resulting in local sliding, which causes severe friction at the upper and lower ends of the bearing, promoting local wear. Therefore, it becomes difficult to satisfy the requirement of durability of the pinch roller.
In a structure such as shown in FIG. 3, it is possible that the roller body is largely inclined not only with respect to the direction of the capstan but also with respect to the direction of the running tape, orthogonal thereto. When the roller body in inclined significantly in the direction of tape running by some cause such as vibration or shock at the time of mode switching, the roller body and the capstan will be in point contact and not in line contact. In this case, pressure is not applied uniformly in the widthwise direction of the tape pinched therebetween, causing irregular stretch of the tape. In addition, the wow and flutter are increased because of snaking or upward/downward movement of the tape, so that it is difficult to satisfy the tape running stability.